The pattern-dependent chirp characteristics of an intensity modulated optical source significantly impact its performance in long-haul lightwave systems. Externally modulated lasers (EML) are routinely tested in the factory to have less than 1 .ANG. wavelength excursion. Conventional time resolved chirp measurements techniques typically used either an optical filter (monochromator) or frequency discriminator (Fabry-Perot, Mach-Zehnder interferometer). Time resolved chirp measurement technique using an optical filter is described in the article by R. A. Linke, "Modulation Induced Transient Chirping in Single Frequency Lasers," IEEE J. Quantum Electron., vol. QE-21, no. 6, pp. 593-597, 1985. Time resolved chirp measurement technique using a frequency is described in the articles by N. S. Bergano, "Wavelength Discriminator Method for Measuring Dynamic Chirp in DFB Lasers," Electron. Lett., vol. 24, no 20, pp.1296-1297, 1988 and R. A. Saunders, J. P. King and I. Hardcastle, "Wideband chirp measurement technique for high bit rate sources," Electron. Lett., vol. 30, no 16, pp.1336-1337, 1994. The first technique, referred hereafter as the classical method, scans the optical filter around the source wavelength and several traces are recorded in order to calculate the chirp. The second technique calculates the chirp from measurements at two or three settings of the frequency discriminator.
While such prior art measurement techniques have been successful they need to acquire several traces for different optical filter positions and require post-processing of the traces to calculate the chirp characteristic.